The present invention relates to processes for forming coatings on ceramic substrates, as well as the products of such processes.
Ceramic materials are finding an ever-increasing number of uses due to their ability to provide desirable mechanical properties while being relatively light weight. One use that has become very important is in machine parts, where a workpiece must undergo repetitive contact with other objects, and thus must be capable of withstanding impact, friction, and/or wear. It is known that the utility of such workpieces, made of metal or ceramics, can be enhanced by providing them with coatings which will increase their superficial resistance to friction, wear, corrosion, impact, or the like.
Among the considerations in selecting or developing a desirable coating are the hardness, strength, and thermal stability of the coating; the chemical reactivity and thermal expansivity of the interface between the substrate and the coating; and the chemical reactivity of the coating's outer surface. These properties are affected by the microstructure of the coating, which depends on the raw materials used as well as the process used to generate the coating.
In achieving the desired mechanical and other properties in a coating, it is often useful to produce a multilayer coating, rather than a single layer of uniform composition. It is also useful to have a mechanism for eliminating or minimizing defects in the microstructure of the coating.
Although various ceramic coatings which have been previously known have some of the above-described desirable characteristics, there is still a need for improved structures which will have even more desirable properties, for the uses outlined above, as well as for other applications.